1. Field of the Invention
This invention relates to an inspection device for detecting the quality of the filter end face of a filter cigarette as one of quality inspections.
2. Description of the Related Art
Various types of filters of filter cigarettes are known. One of the types of filters of filter cigarettes is a dual filter shown in FIG. 1. The dual filter has a charcoal filter member Fc containing charcoal particles and a white plain filter member Fp and these filter members Fc and Fp are arranged on the same axial line in order from the end of a cigarette C.
Therefore, the charcoal particles are not exposed to the filter end face and the filter end face can be kept white because the filter end face remote from the cigarette C is made of the plain filter member Fp Moreover, no charcoal particle enters the mouth of a smoker when he or she smokes.
The filter end face of the dual-filter-type filter cigarette must be inspected in its manufacturing process. As a result of the inspection, a defective filter cigarette to whose filter end face charcoal particles are exposed or through which charcoal particles are seen must be removed from the manufacturing line.
For example, an optical sensor can be used to inspect a filter end face. The optical sensor emits measuring light toward the filter end face of a filter cigarette and simultaneously receives the light reflected from the filter end face to output a detection signal corresponding to the luminous energy of the reflected light as a voltage signal. The level of the detection signal output from the optical sensor changes in accordance with the stage of the filter end face as shown by a solid line in FIG. 2.
More specifically, the defective state of a filter end face is classified into a completely-defective state and a semi-defective state. A completely-defective filter end face is defined as a filter end face made of the charcoal filter member Fc with no plain filter member as shown in FIG. 3. A semi-defective filter end face is defined as a filter end face with an insufficient length of the plain filter member Fp as shown in FIG. 4. At the semi-defective filter end face, charcoal particles in the charcoal filter member Fc are seen through the plain filter member Fp.
Therefore, in the case of a defective filter end face, the luminous energy of the reflected light returned to the optical sensor from the defective filter end face decreases compared with that of a normal filter end face, and the level of a detection signal of the optical sensor lowers as shown in FIG. 2. Moreover, when comparing a completely-defective filter end face with a semi-defective filter end face, the luminous energy of the reflected light returned to the optical sensor from the completely-defective filter end face, that is, the level of the detection signal of the optical sensor further lowers.
In FIG. 2, the expression "none" represents the level of a detection signal output from the optical sensor or the base level when no light is reflected from a filter end face, that is, when no filter cigarette to be inspected is present.
A filter cigarette with a defective filter end face must be excluded because it is a defective product. Therefore, the optical sensor is electrically connected to a comparing circuit and the comparing circuit receives a detection signal output from the optical sensor. The comparing circuit has a criterion for determining whether the filter end face of a manufactured filter cigarette is normal or not, and the level of the criterion is set between the level of the detection signal showing a normal filter end face and the level of the detection signal showing a semi-defective filter end face, as shown by the broken line in FIG. 2. Therefore, the comparing circuit compares the detection signal received from the optical sensor with the criterion and outputs an exclusion signal when the level of the detection signal does not exceed the criterion. A defective filter cigarette is excluded from a manufacturing line based on the exclusion signal.
The optical sensor of the type described above has an aperture for emitting measuring light to the filter end face of a filter cigarette to be inspected and receiving the light reflected from the filter end face. When dust paper and white dust of filter members produced during manufacturing of filter cigarettes enters the aperture and is deposited, the light reflected from the deposit of the dust is added to the light reflected from the filter end face to be inspected. Therefore, as shown by one dot chain line in FIG. 2, the level of the detection signal output from the optical sensor becomes higher than the level of the detection signal corresponding to the light reflected only from the filter end face shown by the solid line in FIG. 2.
The difference between the level of the detection signal showing a semi-defective filter end face and the criterion is small. Therefore, when the optical sensor receives the light reflected from the above-mentioned white deposit in addition to the light reflected from the semi-defective filter end face, the level of the detection signal of the optical sensor exceeds the criterion. In this case, the comparing circuit determines the defective filter cigarette as a normal filter cigarette, and thus a defective filter cigarette cannot accurately be excluded.